See if your starting engagement is too tight - also be sure to check the oiler holes for crankshaft to clutch bell lubrication as rubber debris will tend to clog them. You then end up with a seized clutch to shaft situation. One thing I have noticed is how picky these clutches are when they aren't clean or if the oil level isn't high enough, I would increase the oil level before trying any synthetics if any synthetics at all since it is possible they can break down the chemical bonds in the rubber and cause swelling. Further, more slipping of the clutch, especially revving much higher than the normal RPM range of engagement will cause large amounts of heat on any large hill which will cause you to smear the inside of the clutch bell with melty rubber - it will then immediately start being sticky (also rubber filled oiler holes, crankshaft seizure, lots of damage). Avoid slipping up over a quarter of your RPM range - you want a comfortable takeoff, not a clutch eating machine.